Various wind shear detection systems are known. Among these systems are ground based systems, such as those that utilize a plurality of wind speed and direction measuring stations placed about an airport in conjunction with a system for analyzing the magnitude and direction of the wind at the various stations to provide an indication of a wind shear condition. U.S. Pat. Nos. 4,058,010 and 4,152,933 are examples. Other ground based systems utilize Doppler radars located near the airport (see U.S. Pat. No. 3,427,581).
Airborne systems are also known. Among these systems are systems that compare air mass derived parameters, such as air speed, with ground speed derived from a radar system. In the event of a rapid change in air speed relative to ground speed, a wind shear condition is indicated. Other systems compare air mass derived signals with inertially derived signals to generate a signal representative of wind shear when the rate of change of inertially derived parameters varies from the rate of change of air mass derived parameters by a predetermined amount. Two such systems are disclosed in U.S. Nos. 4,012,713 and 4,079,905. Both of these patents disclose systems that compare a longitudinal accelerometer signal that has been corrected for the effect of gravity with an air speed rate signal and provide a wind shear warning signal when the difference between the accelerometer derived signal and the air speed derived signal exceeds a predetermined amount. The '905 patent also takes into account a downdraft drift angle that is a function of vertical acceleration and air speed. Still other systems monitor the rate of change of deviation from a glide slope beam or an ILS beam to provide a signal representative of wind shear.
While all of these systems do provide some indication of wind shear, the ground based systems are responsive only to conditions in the vicinity where the transducers are placed, and are not responsive to dangerous types of wind shear such as microbursts which form and dissipate rapidly. A microburst is an intense downdraft of cool air that, in some cases, drops 3,000 feet in two minutes. Such systems do not necessarily provide a timely warning to the pilot.
While airborne wind shear protection systems are more responsive to conditions in the vicinity of the aircraft than are ground based systems, many of them require Doppler Radar, an Inertial Navigation System, glide slope signals, or other signals that are not available on older or small aircraft. In addition, it is desirable to develop not only a warning of degraded aircraft performance, but also timely guidance to the pilot on how to safely fly the aircraft during this degraded performance condition, such as a wind shear condition.
There also have been teachings as to how aircraft performance is affected by wind shear (i.e., U.S. Pat. Nos. 4,043,194; 4,129,275; 4,281,383; 4,342,912 and 4,336,606). These teachings involve systems which are often difficult to implement in an aircraft cabin environment, may require the use of special sensors, or do not provide usable information in a timely manner.
Some systems have been devised which not only combine the detection of wind shear but also guidance information to the pilot. In U.S. Pat. No. 4,189,777, air speed rate is used to detect a wind shear condition and, in response thereto, a ground proximity warning system Mode 1 warning curve is modified to increase warning time. Another approach is reflected in U.S. Pat. No. 4,347,572. There, angle of attack, stick-shaker value, vertical speed, air speed, flap position and thrust are used to provide climb-out guidance on a pilot flight director display by indicating an appropriate pitch angle. U.S. Pat. No. 4,040,005 teaches a servo driver composit situation analyzer. There, a complex mechanical instrument is disclosed which, in one embodiment, displays angle of attack flight path angle relative to an aircraft reference and a runway. The suggestion is also made that a CRT display may be used in lieu of the mechanical display. However, the displayed information amounts to a presentation of deviations from desired values of angle of attack and desired flight path. More importantly, since it depends on the pilot to insert a desired value for the angle of attack, it has the potential for giving misleading information during rapidly changing flight conditions. The complexity of the display also makes it likely that the pilot will not use it during emergency situations wnen the aircraft is in sight of the ground.
In view of some recent aircraft accidents which have been attributed to wind shear and in view of maintaining the public's confidence in commercial aircraft, an aircraft instrument which provides timely guidance information to the pilot of tne aircraft so as to enable him to correctly guide the aircraft in a wind shear condition would be an instrument that would satisfy a clear long-felt need.
The fact that so many instrument systems and guidance systems have been proposed, and no one system has yet found acceptance by the industry, is an indication that these prior systems have been unsatisfactory and that the problem of providing guidance information to an aircraft pilot during a wind shear condition is one which has, so far, gone unsolved by the best minds in the industry. Clearly, a new approach to the problem is needed.